Foxtail Millet as a Model for Switchgrass – Comparative Relationships

Switchgrass (Panicum virgatum) is a perennial C4 grass that has gained attention for its potential as a dedicated biomass crop. Two ecotypes, lowland and upland switchgrass, can be distinguished based on plant morphology and region of adaptation. Genetic linkage maps have been constructed in both a lowland cultivar, “Alamo” (genotype AP13), and an upland cultivar, “Summer” (genotype VS16). The lowland (AP13) map consists of 515 loci in 18 linkage groups and spans 1,733 cM. The upland (VS16) map arranges 363 loci in 17 linkage groups and spans 1,508 cM. Overall, the lowland and upland maps are highly colinear and display similar recombination levels. Comparative analysis of the switchgrass genetic maps with the genome sequence of foxtail millet (Setaria italica) identified considerable synteny between the two genomes. Nevertheless, a number of rearrangements were identified, some of which occurred in the switchgrass genome while others are specific to the foxtail millet genome. We are currently exploiting the relatively close relationship between the A genome of switchgrass and the E genome of species belonging to section Rudgeana within the genus Panicum to determine the subgenome (A or B) origin of the linkage groups. Knowledge on the subgenome origin of the linkage groups will assist with the assembly and analysis of the switchgrass genome sequence. In addition to providing anchor points for the genome assembly, the genetic maps will be used to identify quantitative trait loci associated with biomass and quality traits.